In order to improve the energetic efficiency in internal combustion engines, in particular in vehicle applications, efforts are underway to utilize the heat energy, which is contained in the exhaust gas of the internal combustion engine. A possibility of utilizing the heat energy contained in the exhaust gas is utilizing so-called thermoelectric modules, which can convert a temperature difference into electric voltage or a heat flow into an electric current. Such thermoelectric modules operate according to the so-called Seebeck effect, which corresponds to an inversion of the so-called Peltier effect.
A thermoelectric module comprises a hot side and a cold side and can convert thermal energy, i.e. heat into electrical energy during operation. By feeding heat to the hot side and discharging heat on the cold side a heat flow can be conducted through the respective thermoelectric module which is converted into electric current in the thermoelectric module. In order to be able to supply the hot side with heat and the cold side with cold, a thermoelectric module can be practically integrated in a heat exchanger, which comprises at least one heating tube for conducting a heating fluid and at least one cooling tube for conducting a cooling fluid. The thermoelectric module is then arranged between such a heating tube and such a cooling tube so that the heating tube is located on the hot side of the respective thermoelectric module and the cooling tube on the cold side of the respective thermoelectric module. For this purpose, the heating tube, the thermoelectric module and the cooling tube are stacked onto one another in a stacking direction, thus forming a stack.
In the case of such heat exchangers, into which the at least one thermoelectric module is integrated, it has been shown that the heat transfer between the tubes and the respective thermoelectric module can be significantly improved when the stack is preloaded in the stacking direction. Through the preload, areal contacting materializes between the contact surfaces provided for contacting, which makes possible a largely homogeneous heat transfer over the respective contact area. Problematic in this case is that the heating tubes and the cooling tubes are practically produced with comparatively small wall thicknesses in order to improve the heat transport through the tube walls. However, the compressive strength of the tubes is reduced because of this. In order to be able to nevertheless realize the desired preload in the stack, different approaches are possible in principle. For example, support structures can be introduced into the tubes which stiffen the tubes from the inside. Additionally or alternatively, it is possible to concavely curve the tubes on their tube outside facing the respective thermoelectric module towards the thermoelectric module, wherein this curved outside during the clamping of the stack is compressed with a flat module outside facing the respective tube, as a result of which the curved tube outside is flattened and lies flat against the flat module outside.
With an excessive preload there is additionally the danger in principle that the tube outside buckles and because of this concavely curves towards the respective thermoelectric module, as a result of which contacting is largely cancelled out. In this case, too, support structures can be again arranged in the respective tube in order to avoid such buckling of the respective tube. Inserting support structures however is connected with comparatively major effort. In addition, quite close tolerances have to be maintained here so that the support structures can guarantee the desired geometry of the respective tube.